Coal's toxic legacy to the Arctic

Heavy metals accumulate in a number of Arctic animals including the beluga

Coal burning in western Europe and North America has been a prime source of heavy metal pollution in the Arctic.

Scientists plotted levels of thallium, cadmium and lead in a Greenland ice core and linked them to other chemicals indicating coal as the main origin.

Clean air legislation has reduced the heavy metal load in recent years.

But writing in Proceedings of the National Academy of Sciences (PNAS), the team says increased coal burning in Asia may see levels of the metals rise.

There's been very little study of thallium in the Arctic

Dr Joseph McConnell

These substances accumulate in the bodies of plants and animals living in the region, including whales, polar bears and caribou.

Some Arctic people also carry high levels of the heavy metals, which can cause a number of medical conditions, in their bodies.

Economic drivers

The study team, from the Desert Research Institute in Reno, US, analysed an ice core extracted in Greenland which gives a continuous record of pollutants deposited from the atmosphere back to 1772.

They took readings of heavy metal levels on a month-by-month basis.

Clean air legislation in Europe reduced heavy metal input to the Arctic

Graphs show all three metals soaring between 1850 and 1900 as the industrial age took off. The early 20th Century saw inputs 10 times higher than in pre-industrial times.

The Great Depression of the 1930s saw levels dip as economies contracted, then a rise as the global marketplace recovered.

But by the 1970s, all three of the metals were decreasing in abundance, broadly coinciding with the adoption of clean air legislation in Europe and North America, the source regions for most of the input to the Greenland ice.

"In North America and western Europe, there was a big effort to clean up the air," noted lead researcher Joseph McConnell.

"Part of that was a shift from coal to oil and gas, and part was a move to burn coal at higher temperatures and burn it in a better way," he told BBC News.

The rises and falls correlate well with fluctuations in the amount of black carbon and sulphur, products of coal burning, captured in the ice, suggesting that coal was the dominant source of these emissions.

The one blip came from lead which showed a renewed rise in the 1950s, probably due to the swift increase in motoring.

Potent poison

Heavy metals are among substances that bio-accumulate; when they pass into animals, they stay there, immune to digestion and the body's waste removal processes.

When that animal is eaten by another higher up the food web, the predator, whether human or not, generally takes on a substantial part of the toxic cargo.

Most of the studies on Arctic peoples have concentrated on mercury, another heavy metal also produced by coal burning and other industries.

Caribou are among the Arctic animals eaten by indigenous peoples

They suggest that mercury may have contributed to neurological impairment in some communities.

Some Arctic dwellers have been found to receive levels of cadmium above recommended safe limits through their diet. The metal's most important medical impact is kidney damage.

"There's been very little study of thallium in the Arctic, though," said Dr McConnell.

Thallium is a potent toxin.

Once incorporated into rat poison, its use is highly restricted. It was an early suspect in the race to determine what killed former KGB agent Alexander Litvinenko in London two years ago.

The new study promises to help investigators studying the health of Arctic peoples by providing a detailed record of heavy metal input to the environment over time.

Whereas previous studies suggested the cadmium load was highest in the 1960s and 1970s, the new research shows the peak input occurred decades earlier.

As the global population increases, economies develop and natural gas supplies peak, the International Energy Agency predicts coal usage will increase globally, with the major Asian economies including China and India responsible for most of the increase.

Dr McConnell believes the picture of the last few years captured by his Greenland core suggests this renewed interest in coal burning is leading to an upturn in heavy metal input to the part of the Arctic he has studied.

But he believes more cores are needed from different regions, and is proposing to drill in other parts of the Arctic, notably areas north of Russia and east Asia, to establish the global pattern.

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